1. Field of the Invention
The present invention relates to corrugated paper board manufacture and to the belts required by the machines used to manufacture that variety of paper board. More specifically, the present invention relates to the belts that may be used on the single-facer section of a corrugated board production line.
2. Description of the Prior Art
In the manufacture of corrugated paper board, a so-called core paper is heated by steam, which makes it more pliable, and is then fed into a nip formed between a pair of toothed rollers whose teeth mesh, thereby corrugating the core paper in a uniform, undulating pattern. Starch paste is subsequently applied to the crests of the corrugated core paper, which is then mated to a liner paper in a press nip. There, the corrugated core paper and liner paper are bonded together to form a completed sheet, which can then be further processed as desired.
In one machine used for this purpose in the prior art, the press nip is formed by one of the toothed or corrugating rolls and a pressure roll. In another machine of a more recent design, the press nip is extended in the running direction through the use of a press belt instead of a pressure roll. The press belt holds the corrugated core paper and liner paper together against the corrugating roll for a significant portion of its circumference.
The press belt experiences severe operating conditions. Because heat is used to vaporize moisture in the core paper, the belt operates in a high-temperature environment. Further, the belt continually runs against the teeth on the corrugating roll to develop the required bonding pressure between the core paper and the liner paper. Moreover, the belt must be flexible yet have lengthwise strength and widthwise rigidity sufficient to withstand wrinkling, which may cause the belt to drift undesirably from side to side.
Steel belts, that is, belts woven from steel wire, have been proposed for use on this kind of machine. Steel belts are strong and rigid, but are prone to flex fatigue. Moreover, steel belts cannot be woven endless and must be seamed into endless form, the seam being a weak point in the endless belt. Were such a belt to fail, injury to personnel and damage to equipment may result.
European Publication No. 0 630 739 A1 shows a belt intended for use in place of a steel belt on a belted single-facer machine. The belt is endless, and has an inside surface, an outside surface, a length (L) and a width (W). The belt has an endless woven inner layer, an elastomer layer outside of the endlessly woven inner layer, a canvas outer layer that is expansible lengthwise of the belt outside of the elastomer layer, and a coating on the canvas outer layer. The coating is exposed on the outside surface of the endless belt and resists the bonding of foreign material thereto. The canvas outer layer is not endless, but includes two or more sections joined to one another with overlapped seams.
Experience has shown that the belt disclosed in this publication performs poorly in the environment of the machine. The belt is a composite structure which includes an endless inner fabric layer and a canvas outer layer. The two layers have different stress-strain behaviors under tension. In use, the belt is placed under very high operating tensions in excess of 200 pli (pounds per linear inch). As the belt travels around a closed loop and as the individual fabrics are tensioned simultaneously but occupy different path lengths, delamination becomes likely. Moreover, the belt is very rigid, stiff and incompressible, making it difficult to track and guide in operation.
The present invention provides a solution to the problems inherent in the use of a belt of the foregoing variety.
Accordingly, the present invention is an improvement for a single-facer section of a corrugated board production line of the foregoing type in the form of an unlaminated single-facer belt.
The unlaminated single-facer belt has a single base structure in the form of an endless loop lacking a seam and having an inside and an outside, a machine, or running, direction and a cross-machine direction. The base structure is formed by machine-direction and cross-machine-direction yarns, and is either woven from these yarns or is a nonwoven structure assembled from them.
At least one layer of staple fiber material is needled into the outside of the base structure and extends at least partly therethrough.
Finally, the base structure and staple fiber material are impregnated with a polymeric resin material.
The yarns of the base structure, the staple fiber material and the polymeric resin material are all of high-temperature-resistant materials.
The present invention will now be described in more complete detail with appropriate reference being made to the figures identified below.